In general, a conventional internal boring manufacture that requires a mirror-like surface effect on the surface roughness has to go through three cutting tools: a coarse boring cutter, a fine boring cutter and an internal microller burnishing tool. The coarse boring cutter carries out a coarse boring operation and reserves ψ0.2˜0.3 mm for a fine boring manufacture, and the fine boring cutter completes a fine boring operation by a feed rate of f=0.04˜0.1 mm/rev and reserves ψ0.02˜0.04 mm for the polish by the internal microller burnishing tool, such that a mirror-like surface effect with a surface roughness up to Rmax=0.04˜1.2 μm can be achieved. This manufacturing method is used extensively for a high precision having a strict requirement on the diameter of a hole including the hole of a bearing of a device with relative movements such as a cylinder hole.
The aforementioned internal boring manufacture for achieving a surface roughness with a mirror-like surface effect needs to employ three cutting tools mainly because a general boring cutter cannot complete the mirror-like surface manufacture directly, and thus it is necessary to use an internal microller burnishing tool to complete the mirror-like surface manufacture. The main reasons and their drawbacks are described as follows:
Referring to FIG. 6 for a conventional disposable cutting insert for a boring cutter 50, a side cut angle θ1 is defined between a side blade edge 51 and a vertical line of the disposable cutting insert 50, and an end cutting edge angle θ2 is defined between a front blade edge 52 and a horizontal line, and the side blade edge 51 is linear to the front blade edge 52 and connected to a cutting edge 53. If the disposable cutting insert 50 performs a boring or cutting operation as shown in FIG. 7, then the boring cutter 500 will remove the material of a work piece 60 by the front blade edge 52 and the cutting edge 53. After a surface 61 of the internal periphery of the work piece 60 is cut, the surface roughness is correlated with the radius R of the cutting edge 53 and the feed rate f. Referring to FIG. 8 for the surface roughness of a cut surface, the manufacture conditions include (a) The radius of cutting edge R=0.4 mm; and (b) The feed width f=0.07 (mm/rev). According to the equation for calculating the manufacturing roughness Rmax≈(f2)*1000/(8R) μm, and the foregoing manufacture conditions, the roughness Rmax=(0.072)*1000/(8*0.4)=1.53 μm can be obtained, and it belongs to the category of a fine manufacture. Although the surface is smooth and bright, the requirement for a mirror-like surface manufacture (Rmax=0.1 μm) cannot be met, and thus it is necessary to use other surface manufacture cutters to achieve the roughness (Rmax smaller than or equal to 0.1 μm) for the mirror-like surface manufacture.
Referring to FIG. 9 for a schematic view of a general internal microller burnishing tool, the internal microller burnishing tool 60 is applied to the internal periphery of a work piece that requires a mirror-like surface manufacture and enhance the surface roughness. In FIG. 10, an internal microller burnishing tool 60 press a surface peak of the work piece surface by an extrusion method. Although such method can achieve the mirror-like surface effect and lower the surface roughness, its application still has the following drawbacks:
1. During the manufacture, it is necessary to change the internal microller burnishing tool, and thus this method incurs a longer manufacturing time and a higher cost.
2. The cost of the internal microller burnishing tool is high, and thus the manufacturing cost is naturally high as well.
3. After the internal microller burnishing tool has been used for many times, bits produced by the extrusion will be accumulated in the roll beads (cylinder), and it is necessary to clean the tool from time to time. However, a small amount of bits will remain, and the remained bits will be extruded and adhered onto the surface of the work piece and produces a friction with the surface that may blacken the manufacturing surface.